//=============================================================================
// System  : MatchKit
// File    : HexPattern.cs
// Author  : Fabio Bussu  (matchkit@fabiobussu.it)
// Updated : 04/16/2013
// Note    : Copyright 2013, Fabio Bussu, All rights reserved
//
// This code is published under the Microsoft Public License (Ms-PL). A copy
// of the license should be distributed with the code.  It can also be found
// at the project website: http://matchkit.codeplex.com. This notice, the
// author's name, and all copyright notices must remain intact in all
// applications, documentation, and source files.
//
// Version     Date     Who  Comments
// ============================================================================
// 1.0.0.0  04/16/2013   FB  First draft
//=============================================================================
using System;
using System.Linq;
using System.Runtime.Serialization;

namespace MatchKit.Patterns
{
	/// <summary>
	/// Provides the logic to match an hexadecimal string, prefixed by <b>0x</b>.
	/// </summary>
	/// <threadsafety static="true" instance="false" />
	/// <serialization binary="false" contract="true" />
	/// <example>
	///		<code lang="C#" source="..\MatchKit.Doc.Samples\PatternsSamples.cs" region="HexPattern 1"
	///			title="The following example demonstrates how to use the HexPattern class." />
	/// </example>
	#if DC
	#if DC
	[DataContract]
	#endif
	#if SZ
	[Serializable]
	#endif
	#endif
	#if SZ
	[Serializable]
	#endif
	public sealed class HexPattern : BasePattern
	{
		/// <inheritdoc />
		protected override Match OnMatch(MatchContext context)
		{
			if (!context.Is('0') || context.Peek() != 'x' || !IsHexChar(context.Peek(2)))
				return Error(context);

			context.NextFor(2);	// skip '0x'
			var capture = new Capture(context, true);
			context.NextTo(ch => IsHexChar(ch));
			var captured = capture.ToString();

			// i caratteri devono essere pari
			if (captured.Length % 2 != 0)
				return Error(context, "Hexadecimal string length must be even");

			return Success(context, HexToBytes(captured));
		}

		/// <inheritdoc />
		public override string HelpString
		{
			get { return "Hex value (0x)"; }
		}

		private static bool IsHexChar(char ch)
		{
			return char.IsDigit(ch)
				|| (ch >= 'a' && ch <= 'f')
				|| (ch >= 'A' && ch <= 'F');
		}

		private static byte[] HexToBytes(string captured)
		{
			return Enumerable.Range(0, captured.Length)
					 .Where(x => x % 2 == 0)
					 .Select(x => Convert.ToByte(captured.Substring(x, 2), 16))
					 .ToArray();
		}
	}
}
